It's hard to go wrong with a musical revue of 70's songs. Okay, actually a lot could go wrong: pitch problems, poor song selection, technical difficulties, weak performances. Fortunately, though, the Circa 21 Dinner Playhouse's 8-Track: The Sounds of the 70's suffered only a handful of pitch issues and a few missed microphone cues on Thursday's opening-night performance, and otherwise mirrored the fun of the decade's music.